In recent years the use of radiological examining equipment to make measurements of bone density in patients has continually increased. In particular, the use of such equipment in diagnosing and analyzing osteoporosis has become prevalent in the medical community. Osteoporosis is characterized by the gradual loss of bone mineral content or atrophy of skeletal tissue, resulting in a corresponding overall decrease in average bone density. Such a condition is common in elderly women and greatly increases the risk of fracture or similar bone related injury.
The presently available techniques for the radiological measurement of bone density utilize a rectilinear scanning approach. In such an approach, a radiation source, such as a radionuclide source or an x-ray tube, and a point detector are scanned over a patient in a raster fashion. This scan results in an image which has been derived from the point-by-point transmission of the radiation beam through the bone and soft tissue of a patient. The calculation of the bone-mineral concentration the (xe2x80x9cbone densityxe2x80x9d) is usually performed by a dual energy approach.
The rectilinear scanning approach is generally limited by its long scanning time and its lack of good spatial resolution. The poor spatial resolution results in an inability to provide an image displaying high anatomical detail and which will permit accurate determination of the area in the scan occupied by bone. Moreover, the output of the x-ray source and the response of the detector must be closely monitored in order to assure high accuracy and precision.
In accordance with the present invention, a bone densitometry apparatus is provided for examining a subject""s body. A single or dual energy x-ray source directs a beam of x-ray radiation toward the subject""s body. The radiation is applied to the entire region of the body being examined. A scintillation screen receives the x-ray radiation passing through the body of the subject, and emits radiation in the visible spectrum with a spatial intensity pattern proportional to the spatial intensity pattern of the received x-ray radiation.
A charge coupled device (CCD) then receives radiation from the scintillation screen. This CCD sensor generates a discrete electronic representation of the spatial intensity pattern of the radiation emitted from the scintillation screen. A focusing element between the screen and the CCD sensor focuses the scintillation screen radiation onto the CCD sensor. To prevent ambient radiation from reaching the CCD sensor, the present embodiment employs a shade or hood surrounding a region between the scintillation screen and the CCD sensor. A CCD controller then processes the electronic representation generated by the CCD sensor, and outputs corresponding image data.
A dual photon x-ray source is used to allow the examination to be performed with x-rays at two different energy levels. This source can be an x-ray tube, or a radionuclide source with a filter element to remove one of the energy levels when desired. Correlation of the image data retrieved using each of the two x-ray energy levels provides quantitative bone density information.
A focusing element between the scintillation screen and the CCD sensor can take the form of a lens or a fiber optic reducer. An image intensifier can be used in conjunction with the CCD sensor. The image intensifier can be a xe2x80x9cproximity typexe2x80x9d image diode or a microchannel based device. It can also be directly attached to the CCD. An image storage device used with the CCD controller allows manipulation of the CCD sensor output signals by a data processor. This includes the correlation of measurements utilizing x-ray beams of two different energy levels. The system can also be adapted to operate at higher shutter speeds enabling the counting of x-ray transmissions. This provides energy measurements of x-ray transmissions that are useful in certain applications.
In an alternative embodiment, a detector made of amorphous silicon is used to receive and detect the radiation from the scintillation screen to generate the electronic representation of the spatial intensity pattern of the received x-ray beams. The amorphous silicon detector can replace the CCD detector or it can be used to receive the x-rays directly.
In another preferred embodiment, the apparatus of the invention includes two scintillation screens, each of which is associated with its own respective CCD detector or amorphous silicon detector. One of the scintillators is reactive to high-energy x-rays and generates an optical image of the spatial intensity pattern of the high-energy x-ray pattern. Its associated detector detects the image and generates an electronic representation of the high-energy x-ray pattern. The other scintillator is reactive to low-energy x-rays to simultaneously generate an optical image of the low-energy pattern. Its associated detector generates an electronic representation of the low-energy x-ray pattern. The data processor performs the correlations of the measurements for the x-rays at two different energy levels.
An additional preferred embodiment is directed to systems and methods of imaging spectroscopy where a charge coupled device (CCD) is optically coupled to a scintillator and measures or counts the spatial intensity distribution of a radionuclide that has been introduced into bodily tissue, either in vivo or in vitro. CCD""s of sufficient thickness can be used to measure gamma ray events without the use of a scintillator in certain applications. The CCD has sufficient resolution and sensitivity to measure such distributions accurately, usually in less than two minutes. Radiation sources that emit radiation having an energy in a range between 10 and 2,000 keV, and preferably in the range between 20 and 600 keV, are delivered to the cancerous tissue or any other suitable pathologic abnormality.
The CCD acquires xe2x80x9cframesxe2x80x9d of information by counting the number of gamma-ray events over a selected period of time. Each frame, or a sequence of frames that have been added or summed to provide an image, can be filtered using pulse height analysis techniques to substantially reduce or eliminate scattered radiation. Pulse height analysis can also be utilized to discriminate between signals having different energy levels that contain diagnostically significant information. The system""s discrimination and energy measuring capabilities render it suitable for diverse applications.
An optical storage element such as photostimulable phosphor can be used with the imaging area detectors described herein to perform x-ray imaging and quantitative analysis. The optical storage system described herein uses an x-ray source to generate x-rays that are transmitted through the object to be imaged and/or scanned. The optical storage element collects the transmitted x-rays, where the spatial distribution of the collected information is correlated with the density distribution of the object. The storage element is then illuminated by a second light source, such as a laser or a high power broadband source, to induce the emission of the stored optical energy distribution. The emitted optical distribution is detected by an area detector to provide an image of the object. This has a variety of applications in both bone and soft tissue imaging and in particular for digital dental radiography.
Another preferred embodiment of the invention provides a method of fabricating a pixelated filter structure of dual energy imaging applications. This procedure uses microfabrication techniques to fabricate a thin film filter with an area detector to simultaneously collect two different energies in an x-ray imaging system. This is particularly well suited to flat panel detectors such as CCDs having small pixel sizes.